MicroRNAs are a new class of non-coding small RNAs that negatively regulate gene expression by either degrading mRNA or suppressing protein translation. A miRNA cluster, miR-15/16, has been implicated in a variety of human diseases, such as cancer, and embryonic development. In particular, miR-15/16 was found to target the receptor Acvr2a, a core component of the Nodal signaling pathway, which is well-known to control embryogenesis. To gain more insight into this cluster's role in development and human diseases, the investigator proposes to generate two transgenic rat models: one is a ubiquitous transgenic rat (UBC-miR-15/16) that expresses miR-15/16 in all tissues using a human ubiquitin C promoter (UBC) in a lentiviral vector;Second is a tetracycline(Tet) inducible transgenic rat (Tet-miR-15/16), in which miR-15/16 cluster will be driven by Tet regulated lentiviral vector. The Tet-miR-15/16 transgenic rat will be crossed with a transgenic rat, Rosa26-rtTA-M2, that the reverse transactivator rtTA-M2 was driven by a ubiquitous promoter Rosa 26 the investigator generated in his laboratory recently to obtain a conditional double transgenic rat that expresses both the miR-15/16 and rtTA-M2. The expression of miR-15/16 cluster in this double transgenic rat will be tightly controlled by the doxycycline. This double transgenic rat model will provide an alternative approach to study the biological functions of miR-15/16 if the UBC-miR-15/16 transgenic rat model displays an embryonic lethal phenotype. The investigator will characterize these transgenic rats by genotyping, phenotyping of embryos, postnatals, and adults at different developmental stages using molecular biological, histological, and immunohistochemical approaches. Those two models will be highly valuable to address the molecular mechanisms by how miR-15/16 cluster is involved in multiple signaling pathways in development and other human diseases. PROJECT NARRATIVE: The ubiquitous and tetracycline inducible transgenic rats expressing miR-15/16 cluster will be generated to investigate their roles in development and other human diseases.